Walk into a tool supply and you'll find HSS drills described as "standard point," "split point," "parabolic flute," "four-facet," "web-thinned," and a dozen other geometry terms. Most machinists know the split point is better for something, but fewer can articulate exactly what it changes and when it matters.
Point geometry is one of the highest-leverage variables in drilling performance. The same material, same speed, same feed — different point geometry produces meaningfully different results in hole location accuracy, required thrust, chip formation, and drill life. Here's how the major geometries work and when to reach for each one.
The Standard 118-Degree Point
Standard Conical Point — 118° Included Angle
The baseline geometry ground on most general-purpose HSS jobber drills. Two cutting lips at 59 degrees each meet at the chisel edge. The chisel edge scrapes and extrudes material at the center of the hole rather than cutting it, which is the primary source of the thrust required to drill. The 118-degree point angle is a compromise that works reasonably well across a wide range of materials.
- General-purpose drilling in mild steel
- Soft materials (wood, plastic, aluminum)
- Manual drill presses where force can be applied
- Applications where center punch location is used
- High thrust from chisel edge
- Tends to walk without center punch
- Inconsistent performance in hard materials
- Requires more axial force than split point
The 135-Degree Point
A shallower point angle — 135 degrees — reduces the length of the chisel edge and changes how the cutting lips engage at entry. The shallower angle distributes the cutting force over a slightly longer lip, which can improve entry on harder materials. Many split-point drills also use a 135-degree base angle because the geometry works better with the additional split-point grinding.
The 135-degree standard point is a modest improvement over 118-degree in harder materials but still has the full chisel edge problem. It's not a dramatic upgrade on its own — the split point modification matters far more than the angle change.
The Split Point (Four-Facet) Geometry
Split Point — 135° with Web Thinning
The split point modifies the standard geometry by grinding two additional facets into the chisel edge, effectively eliminating it and replacing it with two small secondary cutting edges. Instead of scraping at the center, the split point drills at the center. This is the single most impactful geometry change available on an HSS drill.
- Dramatically reduced thrust (50–70% less axial force)
- Self-centering — minimal or no center punch needed
- Better performance in hard materials
- More accurate hole location
- Standard for CNC applications
- Secondary edges wear and are harder to regrind correctly
- Slightly more complex geometry to inspect
- Costs more than standard point drills
- Overkill for soft materials at low speeds
For CNC machining, split point drills are essentially the default. The self-centering characteristic means you don't need a dedicated spot drilling operation before every hole — the split point bit positions itself accurately on entry without a pilot. In a program with 50 drilled holes, eliminating the spot drill operation is a significant cycle time saving.
Web Thinning
As drill bits get reground repeatedly, the point moves back into thicker web — and the chisel edge gets wider. Web thinning is a secondary grinding operation that removes some of the web material to restore a narrow chisel edge on a bit that has been shortened. It's often performed as part of a professional regrind on bits that have had multiple cycles.
A bit with excessive chisel edge width from web growth drills with much higher thrust than when it was new. Web thinning corrects this. It's one of the things a professional regrind on a WinsloMatic handles that a basic bench grinder cannot address — the geometry for web thinning requires a different grinding approach than point regrinding.
Parabolic Flute Geometry
Parabolic flute drills change the cross-sectional shape of the flute from the standard helical groove to a parabolic curve. The parabolic shape provides a larger flute volume and a more aggressive chip-curling geometry that breaks chips shorter and evacuates them from the hole more reliably.
Parabolic flutes are primarily valuable in deep-hole applications — depth-to-diameter ratios of 5:1 or greater, where chip packing becomes the limiting factor rather than edge wear. In short-hole work (under 3:1 depth ratio), the advantage over standard flutes is minimal and doesn't justify the higher cost. In deep holes in aluminum, stainless, or any material that produces long stringy chips, parabolic flutes are a genuine performance upgrade.
Application Summary
- Manual drill press, general steel, soft materials: Standard 118-degree point is adequate. Quality matters more than geometry — a good HSS jobber beats a cheap split-point drill.
- CNC machining, close-tolerance work, hard materials: Split point (135-degree four-facet). The self-centering and reduced thrust are genuine performance advantages.
- Deep holes (>5× diameter), stringy chip materials: Parabolic flute geometry with split point.
- Short-production bit that has been reground multiple times: May need web thinning to restore narrow chisel edge — this is a professional regrind operation.
MachinistPost restores HSS drill point geometry by mail — including split point geometry on four-facet bits and web thinning on bits that have been shortened by prior regrinds. From anywhere in the US, back to you sharp within the week.
Send Your Bits